A basic problem of in-tube burning rockets is the temperature sensitivity of the launch motor. The propellant burning rate is a function of its ambient temperature and increases or decreases with increases or decreases in the firing temperature. This behavior results in two undesirable characteristics in the launch motor design. First, the launch motor must completely burn out in the tube at the lowest firing temperature in which the weapon will be used. This results in a longer launch tube length than that needed for the nominal temperature operation. Since this burning time can be at a value twice that obtained at high temperature, the nominal burning time of the motor must be correspondingly shorter than would be the case without a temperature dependency. A second undesireable characteristic results from the fact that the increased burning rate at high temperatures causes higher chamber pressures which must be accommodated by added weight in the motor case and thus is responsible for further increases to total launch weight. The approach that has been taken in the past to ameliorate this problem is to improve on (lessen) the temperature sensitivity of the propellant thru the use of ballistic additives. While these improvements have resulted in temperature sensitivities that are considerably lower than the early propellants, propellant compromises have been made and some temperature sensitivity still remains.
Therefore, it is on object of this invention to provide a reduction in launch motor temperature sensitivity thru hardware modification rather than propellant formulation by the incorporation of a self-regulating combination of nozzle throats.
Other objects and advantages of this invention will be obvious to those skilled in this art.